Carbon nano materials and graphene in particular are envisioned to be the key materials for future electronics, photonics and related technological areas. Graphene is a two-dimensional material consisting of hexagonal aromatic carbon network. It is ultrathin having a thickness of minimally only one atomic layer and it has excellent electronic properties, including conductivity, making it a potential material to be used in flexible, transparent thin electronic devices.
The problem with pristine graphene is that it has no band gap and thus it is not suitable for electronics as such. What is needed is patterning of graphene with functionalities that allow opening of a band gap and tuning of it and other electrical properties. In this regard, several strategies are being developed. One possibility is to cut graphene into narrow ribbons which have band gap due to quantum confinement and edge effects. Another possibility is to use template growth of graphene nanoribbons. However, it is very difficult and expensive to control graphene ribbons to the required degree of precision.
Laser ablation has been used for making narrow nanoribbons and for patterning graphene and for pattern transfer. In these methods, pulsed lasers were used for cutting graphene via ablation or burning. The processes could be locally controlled by focusing the laser beam to a small diameter. Patterns could be made by moving the sample under laser illumination. The key common factor in these methods is that in all of them laser is used to remove material from graphene sheet. Thus, these methods cannot be used for controlling electrical properties of patterned areas.
In this field, the publication US2009/0311489 discloses a patterning method for a carbon nanotube (CNT) layer. The method is based on focusing a laser beam on the layer and moving the sample relative to the laser beam. The effect of the laser beam is to remove CNT material by ablation or burning, thus this method can only remove material but not change its electrical properties. Thus, carbon nanomaterial with areas of different electrical properties cannot be obtained.
Another strategy involves patterning of graphene oxide (GO). GO is a form of graphene which contains chemical groups with oxygen, typically C═P, O—H and O—O—C groups. GO is made from graphite. GO is insulator and it has to be reduced to reduced GO (RGO) in order to make it conductive to some extent. However, RGO is not the same material as pristine graphene and it does not have as good electrical properties as pristine graphene. Thus, these methods suffice from obtaining carbon nanomaterial with extremely good conductivity and low band gap. Thus, RGO does not have the excellent electrical properties of pristine graphene, e.g. because of the oxidation-reduction process of graphite. Still further, if the oxidation or reduction is made using wet chemistry, the graphite for GO may become contaminated, which further worsens the electrical properties of RGO.
In addition, some of these methods require using equipment with reasonable high investment costs. Still further, the spatial accuracy of some methods is not satisfactory for future electronics requiring a line width in the 500 nm region and below.